The Mucopolysaccharidoses (MPS) are inherited, connective tissue disorders that result from the deficient activities of specific lysosomal enzymes required for glycosaminoglycan (GAG) degradation. Among the various organ systems involved, the bones and joints are severely affected. Although several therapies have been or are currently being evaluated for MPS patients, the positive effects on bones and joints have been limited. In addition, there are no appropriate biomarkers that can be used to monitor the effectiveness of these therapies for bones and joints. The underlying hypothesis of this research is that GAG storage in MPS individuals activates Toll-like receptor-4 (TLR4) signaling pathways, leading to a complex pattern of inflammation, apoptosis and cell proliferation. This, in turn, causes abnormal connective tissue matrix homeostasis, resulting in bone and joint destruction. Three specific aims are proposed in this project using the rat and cat models of MPS Type VI. Aim 1: We will further examine the mechanisms underlying GAG-induced signaling abnormalities in MPS connective tissues by a) using Toll-like receptor 4 (TLR4) reporter cell lines and knock-out mice to evaluate the direct effects of GAGs on TLR4 activation, b) continuing to quantify pro- inflammatory and pro-apoptotic proteins in MPS chondrocyte and synovial cell extracts and media, and c) examining the mechanisms leading to GAG-mediated abnormalities in two important signaling lipids, ceramide and sphingosine-1-phosphate (S1P). Aim 2: We will explore the use of plasma and synovial fluid as sources of biomarkers for the MPS disorders by a) obtaining these materials from MPS VI cats of various stages of disease severity, and comparing the levels of several pro-inflammatory/pro-apoptotic proteins and lipids (ceramide and S1P) to those found in age-matched normal cats. We will also compare GAG levels in plasma and synovial fluid from the MPS VI cats to those found in urine, b) using the MPS VI cat synovial fluid for a proteomics analysis aimed at identifying novel proteins that are abnormally expressed in this disease, and c) obtaining plasma and synovial fluid from human MPS VI patients before and after treatment by intra-articular enzyme replacement therapy, and evaluating the expression of several biomarkers identified from the animal experiments outlined above. Aim 3: Based on our preliminary findings, we will evaluate the efficacy of TNF- inhibitors and anti-apoptotic drugs in the MPS VI rats. Each of the four molecules to be studied has already shown efficacy in animal models of arthritis, and one (Remicade) is clinically available.